THE ROOF LIFTING SYSTEM

4/19/10

Someone would really have a product to sell, coming up with a pre-packaged lift system for these kinds of applications, it seems like everyone is fumbling around trying to come up with the perfect affordable mechanism with pretty much the same requirements, lifts all four corners evenly, somewhat speedily, can lift in somewhat out of level conditions, a manual override sure would be nice, ( It looks like marc at XP campers may have figured this one out) but nooooo, hundreds of hours & thousands of words on-line are spent by everyone designing their own from scratch. I’ll throw mine in the pot for scrutiny as well.

the lift system I’ve designed consists of three basic parts;

the lifting pipe – the part that slides up & down, attaches to the wall & the roof, used in both compression & tension

the linear bearing – the part that keeps the lifting pipe sliding up & down perfectly straight & smooth

the hydraulic cylinder – the muscle behind the movement.. ..duhhh!

THE LIFTING PIPE – is a pretty basic 1 1/4″ hollow pipe except for one thing, because this is a soft side pop up, the cloth needs to fold in when the roof is down, not a problem, as I plan to utilize a bungee around the perimeter similar to the Sportsmobile penthouse roof sides

but unlike the Sportsmobile, my lift needs to be pretty close to the exterior walls not leaving much room (any room really) for the material to fold into. To solve this I designed a 10″deep swoop in the top of the pipe to allow for the cloth with a little help from some internal bungees as well. I’ll adjust the system as it is built, but I’ve figured out how to pull the cloth in as the pipe drops down. This lifting pipe will have mounting plates to the linear bearing, the cylinder, & the roof.

design for the lifting pipe and all mounts, also shows plan view of all three components

I did toy with another design altogether, a hydraulic cylinder that would actuate a big hinge that folded in when down, pulling in & creating room for the material, I even designed this as a nautilus shape to create the same resistance throughout the lifting motion (even the first couple inches, which with a straight hinge would require way more force than the last couple inches) this design was nice & out-of-the-way when up, pulled in the material when down, but had too many moving parts.

the nautilus shape requires the same force to lift the hinge in all positions, a straight hinge would require much more force to start lifting when in the 'down' position

THE LINEAR BEARING – is a drylin W linear guide system, single rail, square rail 48″ long, made by IGUS (you can get any length rail you need)

the lifting pipe will attach to this rail with two bearing that slide up & down freely without allowing any lateral movement, they will however allow for some discrepancy in uneven lift speed between the four corners.

THE HYDRAULIC CYLINDERS – are a complete kit that was custom-built for me by hypac hydraulics in Kentucky, the makers of Alaskan Campers’ lift systems

not only did we create a double-acting system (power up/power down) but this will also have two solenoids to lock the roof in whatever position is desired, holding it up, or holding it down, without the need for latches to hold it down when driving (i didn’t want this from a vandalism & theft standpoint), but I also sent randy there (another randy) my cylinder locations and he’s having all the hose lines & manifolds made as well. This will all be powered by a 12 volt pump, which should be able to lift the roof the 24″ of stroke in 22 to 30 seconds (my goal) all operated by a switch just inside the door.

Now, one aspect of any hydraulic system is that you need to regulate fluid pressure (fluid flow) into the individual cylinders sometimes to equal the individual resistance (weight) to get all four corners to raise at the same speed, this, if the roof weighs more at one end than the other, or, lets say, if you have a cabover design (like I do) where the front cylinders are just behind the cabover part, the front cylinders will take more roof weight than the rear (half the distance between the cylinders, plus the cabover roof weight, where as the rear cylinders take just half the distance between the cylinders) I’ve solved this merely by the placement of my rear cylinders, they are not going to be in the rear corners, but rather toward the front by almost exactly the same distance that the front are back from the front of the cabover roof (the rear cylinders are going to be between the door & the window) this puts almost exactly the same weight onto all four hydraulic cylinders, so resistance, hence pressure, hence speed should be the same. Not only will this solve the speed problem, but moving the rear cylinders out of the rear corners also eliminates the problem of all the material in the corners getting bunched up, as the roof goes down, into a small area.

I lay awake at night thinking about this stuff!

The only aspect I couldn’t get with this system was the manual override, I partially understand the reason; this system has a reservoir tank to hold the fluid when not in the cylinders (typical) and the pump choses to pump into the bottom or into the top of the cylinder dependent on if I want the roof up or down by the direction the pump rotates (simple enough). A manual override would have to bypass the pump, & how do you direct the fluid into either the bottom or top without chosing the direction (or can you manually pump in each direction, so two manual pumps) either way how do you close off the fluid from the electric pump when manually pumping? I think this is just a product of the bi-directional system. If the new XP camper lift has this figured out, I highly suggest talking with marc, or potentially purchasing through him if he’s open to it.

5/2/10

well, I haven’t been the most productive lately, Hypac shipped the hydraulic kit last friday so I should have it this week, randy @ harvest valley is making the lifting pipes, last weekend I ran wires from the engine compartment back into the camper & set up a temporary battery back there to power the steps & hydraulic pump (when i finally get it in). The hydraulic pump draws up to 35 amps, so I ran a 50 amp circuit for the camper. I also ran the wires for the rear winch (on a 70 amp circuit) & got the rear winch powered up. It’s so nice working under this truck, lots of room, everything’s clean.

I also began designing the cabinets inside, just like designing the pivot frame, I was initially intimidated (I don’t know why, I’ve been woodworking for years) but these cabinets aren’t going to be built like home cabinets, no face frames, & I design thinking of how to put it together, I know I want to build curves, so I just couldn’t get my head around the process I wanted to employ – not any more! just like the pivot frame, I’m now past that & into the cocky phase. I now see all the parts in my head, & the order of how to assemble them & get the curves I want. I also designed the ceiling (this sounds wierd, but I plan on doing more than the minimum), I’m planning on indirect mood lighting with either fiber optics or LED rope lights (we are still newlyweds you know!) & having a raised center area that accentuates the curves in the cabinets below. I have however decided against a stripper pole, for working out you know! (Bethany got really disappointed when I told her it didn’t make the cut!)

got the roof off the bullet to spray primer & truck bed liner on the inside for sound deadening, I’ll also be gluing insulation to the inside to further deaden sound. I’m still refining my ceiling design, but plan next week to wire the ceiling, then insulate, then begin the interior face of it. I’m still waiting for the hydraulic package.

spraying etching primer on the raw aluminum ceiling, notice the two skylight locations

be careful, bedliner sprays on FAST, it throws a lot of product in a short time

5/20/10

I finally got all the parts together, along with homemade brackets for the base & top of the cylinders, as well as some time.

Hypac’s package came as a completely assembled unit, all four cylinders were plumbed with just the right length of hose, to a central manifold with the two solenoids for holding the roof up or down (these are normally in the ‘locked’ position, you have to energize one or the other solenoids to ‘unlock the position’ when raising or lowering the roof). I can tell this phase is going to take a little time to make all the adjustments to get things to operate flawlessly. I mounted the linear bearings to the wall panels, temporarily attached the lifting pipes & hydraulic cylinders & powered up the system. Despite my design of equal weight on each of the four cylinders, the front two cylinders (the two closest to the pump) both raised & lowered faster than the two rear cylinders, there must also be additional friction in the added length of hose, so I’ll need to get in-line flow resrictors to slow down the front cylinder speed. I also have to hunt down a momentary contact switch capable of 35 amps to control things. Outside of that, the pipes lifted just the right amount, were at just the right heights up & down, moved smoothly both up & down, ended up in just the right position on the roof edge radius’, & all my math in designing the lifting pipes worked out perfectly in regards to mounting heights for the cylinders, & bearings, so the lifting pipes will get sent off to powdercoating today. I ‘m hoping to chase down these adjustments with a local hydraulic shop today as well.

all the lifting parts temporarily assembled

a cleaner shot

the roof raised in position with the lifting pipes

5/21/10

Although I didn’t get anything done in the shop yesterday, I got plenty accomplished. I chased down a 35 amp momentary contact switch enough to learn that there aren’t any, 20 amps seems to be the most I could find, initially I thought I could use a relay & normal switch, but the bi-directional hydraulic pump requires switching polarities to reverse the motor, & relays are just open or closed.. .. or so I thought. I ended up finding (through some help from a radio engineer) a reversing solenoid relay,

which, based on how I switch it, will send power momentarily (providing you use a momentary contact switch) with the polarity in either direction. really, this is made for just this type of application.

Next, & this may be my biggest contribution to all pop-up expedition builds out there, the uncontrollable part of a hydraulic system discussed in great detail on multiple forums, is the fact that when you have more than one cylinder, you can’t really control the speed that the cylinders lift, as all four (in my case) are tied together within a central manifold & hydraulic fluid chooses the path of least resistance first, so if you have two cylinders that have more weight on them, (like in a cabover design) they have more resistance to raise, so fluid lifts the rear two cylinders first, then when they reach their top & can’t go any more, they have more resistance than the front two cylinders, so fluid starts flowing into the front two cylinders. Coming down is the same, as fluid would flow out of the two front heavier cylinders first then the rear. In line flow restrictors are not a reliable way to deal with this because, as in the above case, you can increase resistance to the two rear lighter cylinders to equal out pressure on lifting, but then on lowering, you’ve also restricted flow on the rear cylinders, slowing down flow, & the front two are already heavier, so they drop even faster, so this just makes things worse. A mechanical screw manifold controls flow into each of the ports, but after talking with multiple hydraulic shops yesterday, we determined that for this type of application, the pressure is too low (as my weight on each cylinder is about 60 lbs), & this mechanism doesn’t do a good job at this low a pressure & slow a speed.

The solution hit me last night, (not while sleeping oddly enough) think about a drafting mayline, or slide rule, as you slide up on one side of the mayline, the other side lifts as well, at exactly the same speed. This is done through two simple cables strung in a simple geometric pattern as to be simple & foolproof

a simple diagram of the cable layout in a drafting mayline

notice how if you move the mayline up, the cable on the bottom left gets pulled as the bottom point is fixed, pulling in on the top right side & vise versa, always keeping the two sides moving together. so simple, with few moving parts.

now in this design, the mayline moves & the side cables stay static, in the bullet however, the side cylinders move, & there’s nothing in the center, so I needed to revise the way the cables run to achieve the same properties.

a simple diagram of the cables in a hydraulic system to keep the cylinders moving together

now remember this is a diagram, as the two pulley at the top would actually be one double pulley, & the two cables going across the top would truly be behind each other. The pulley on the bottom is a single pulley, & the cables mount to the bearing mounts on the lifting pipes (where i’ve shown a right angle). follow the movement as one cylinder moves up, it pulls on the cable that goes down & ends up pulling up on the opposing cylinder, similarly, as you pull one of the cylinders down, the cable going up through the pulleys goes across, down & back up pulling down on the other cylinder. how does this differ from just using cables to lift the roof from one central motor? simple, the force on the cables & pulley is GREATLY reduced as they are not taking the roof load at all, they are merely equalling out the difference in pressures between the two cylinders. if the total weight on both cylinders is about 60 lbs in my case, plus with some additional friction on one cylinder, that cylinder would have lets say about 70 lbs of resistance, a 10 lb difference, the cables would equal out the resistance pulling down on the lighter cylinder with 5 lbs of force, & pulling up on the heavier with the same 5 lbs of force equaling out both cylinders at 65 lbs of resistance. Simple ehh, so the force on the cables & pulleys is tiny. Picture TV cabinet retracting doors, they open up, then slide into the cabinet with the top & bottom parallel at all times, using a similar system as the mayline, look at how tiny those cables are.

Now this design only levels the two side cylinders to each other, not across the two sides of the camper, but each sides conditions are identical, so side to side isn’t a real issue, (& I noticed when I lifted my roof, the two front’s went up & down faster than the two rears, but each side moved the same as the other side. If I had a side to side problem, I could easily adapt this system to run cables across the front wall as well, or even below the floor to the other side.

I plan to use 1/16″ cable, with tiny pulleys mounted behind the lifting pipes, fixed to the floor & the top of the wall panels. The top cables will be pulled through 1/2″ PVC conduit which will be up behind the interior of the wall cap, in the thickness where the insulation goes, hidden behind the interior finished wall panel. The only reason for the conduit is in case I ever have to replace them, I can easily fish them through to the other cylinder. I also plan to use turnbuckles at the bearing mount point to achieve & adjust tension in the cables

just purchased all the materials to do both sides (all four cylinders).. …$32.00 !

6/16/10

Well.. ..took a little bit longer than I expected! but between memorial day camping, & a powder coater with a non-working oven, I find myself in June. The hydraulic system is now in & working perfectly, I can now say that my cable resistance equalizing hair-brained idea works exactly as expected, exactly as I wanted. Each pair of cylinders go up at exactly the same speed, & there is only a slight difference (like about 1 inch or so) of difference from side to side. I initially was going to make a small bracket to mount the cables to the bearing/lifting pipe connection, but realized if I have to remove the lifting pipe for any reason, my cables hang loose, so I wandered through the hardware store untill I chose to drill in the side of the bearing block, thread in a simple thumb screw, drilled a hole into it, provided a plastic hole flange, & mounted the cables right to the bearing block directly, simple, but effective.

The thumbscrew attachment of the cables to the bearing block (all lines need a turnbuckle to tension & adjust the heights)

Actually the whole cable system is really simple, & almost invisible behind the lifting pipes & wall cap. Bethany couldn’t figure out how the pipes were connected when I showed her the equal motion before the cylinders were attached.

the bottom pulley attached to the floor, & my bottom cylinder mount

The reverse polarity solenoid works perfectly & wires up easily, I highly recommend it, not only that, but I ended up reversing the sides of the basement for the equipment. I initially designed the equipment to be on the passenger side, but rethought the location to the driver’s side just above the propane & air tanks & near all the hookups. Now the passenger side is totally for storage (this should make setting up camp a little bit easier as all the equipment is on one side & all the campsite ‘stuff’ is on the other. I also got the automatic step’s remote door switch in & permanently secured all the hydraulic lines to the edges, & set up temporary switches near the door for the steps & lifting system. Building the basement while the top (or dog bed floor) is off was a brilliant idea, no crawling, but I wired & plumbed the hydraulics, temporarily set up the temporary battery there, will mount the air compressor & water pump there, all before the ‘ceiling’ is put on.

the beginnings of the basement, the hydraulic lines & pump are in permanently, the wiring is temporary as the battery will move

You’ll also notice I mounted a second wallboard inside the basement to mount the manifold, solenoid, & hydraulic lines on the way into the basement. This was so I had a good wall to mount to without drilling through my exterior envelope.